There are presently on the market pushbutton switches which are designed using a flexible membrane for controlling electrical contact. These membrane switches typically do not make noise when depressed and because of the relatively slight pressure required to effect contact closure the user is not exactly sure that such contact has been made. This lack of audible feedback, coupled with low tactile feedback, is exacerbated in the situation when the result of the key operation is not otherwise communicated to the user. For example, in telecommunications equipment, it is typical for a central processor to scan the keys of many communication devices "looking" for a key push. Upon detection, the processor begins processing the information while at the same time attending to many other tasks. After a period of time the processor may then acknowledge to the user, via a lighted lamp or the provision of dial tone, that the key push had been recognized and acted upon. This recognition may only take a few tenths of a second, but since immediate positive feedback is not provided, the user may again operate the same key. Thus, it is necessary to provide a feedback mechanism to silent keys when they are used in conjunction with delayed feedback devices.
This problem is compounded in that had the processor been available to provide the desired feedback signal in the first place, it would have been provided. Thus, in situations where processor capacity is not available a feedback signal must be provided which signal must not rely on the processor for its generation. A further requirement for the feedback signal is that it should be uniform from one key push to the next and should be indicative of the fact that the key push has been processed.